John walked into the lab several hours later, dropping his suitcase at the door and with a face like thunder. Sherlock didn't even look up from his work at the lab bench.

'Mycroft?' Kate asked.

'You've been spending too long with him,' John muttered, looking pointedly at Sherlock's oblivious head. 'Yes, Mycroft arrived at the airport and offered, no insisted on giving me a lift back to London in the back of his lovely car, and interrogating me about you the whole way back. He's just returned from the Middle East apparently, so just happened to be in the airport at the time that my plane landed.'

'Sorry,' Kate said, pulling a face, 'I should have realised that he'd get to you too.'

'Whats going on, Kate?' John asked.

'Come into the coffee room, and I'll tell you,' Kate said with a sigh, realising that Sherlock wasn't going to be joining in this conversation any time soon.

...

'Mycroft saw me and Sherlock in a restaurant together on Friday night,' Kate told him as soon as the door had shut behind them.

'Ah,' John said. 'And I take it that he's not best please about this.'

'Apparently not. He's been investigating me, John. He's gone into everything - not just the obvious stuff, my medical records, even my occupational health records, and this evening there was a guy on a motorbike taking photos of us, its ridiculous!'

'What does Sherlock say?'

'He seems to think that Mycroft is going to kidnap me and whisk me off in his car of doom, then brainwash me into breaking up with Sherlock.'

John pulled a face, and then said, 'Kate, how much has Sherlock told you about Mycroft?'

'Quite a bit - why?'

'Those two -' John sighed, then sat down on one of the chairs arranged around the outside of the room. 'They have the strangest relationship. Mycroft can't leave Sherlock alone, its as if he feels responsible for him somehow, but he just can't stop interfering. I think it all stems from the fact that Mycroft was Sherlock's guardian after their parents died, you know that he's seven years older?'

Kate nodded, 'But Sherlock's a grown man, surely Mycroft realises that.'

John sighed, 'You know Sherlock, Kate. He's not always the most - rational person, whatever he may think. And he hasn't always acted in the most sensible way, I don't think. When things go wrong he relies on Mycroft to provide a get out of jail free card, to sort things out for him, so its understandable that Mycroft wants to pre-empt any problems.'

'And is that what I am? A problem?'

Kate sounded curious, John thought, rather than concerned. 'To Mycroft, yes, potentially. Kate you have to understand that in the five years that I've known Sherlock he's never had anything approximating a relationship, or ever even referred to one in the past. Of course Mycroft's worried, wouldn't you be in his position?'

'So what would you do?'

'I would meet with Mycroft,' John said slowly and carefully.

'Seriously?' Kate asked, 'But Sherlock said..'

'Sherlock is wrong.' John said firmly. 'He does get paranoid about things at times, Kate, you must have realised that. And he always paints Mycroft as the bad guy.'

'And he isn't?'

John sighed again, 'He's not a pantomime villain, no. He's just concerned.'

'And you think that if he met me..'

'And realised that you're a sensible, stable individual who cares deeply for Sherlock then he'd be reassured, yes I'm fairly sure that he would.'

'Sherlock would never agree.'

'No, he wouldn't.' John looked at Kate in a way that said everything.

She stared at him for several minutes, taking in what he was saying, then finally shook her head. 'I couldn't, John, not without telling him.'

'Even if it was for the best?'

'I couldn't lie to him, I won't lie to him. Trust is just so important to him, seeing Mycroft behind his back would feel - underhand, thats no way to start a relationship.'

'You really love him, don't you,' John said, trying to keep the surprise out of his voice.

'Of course.'

'Then good luck to you Kate, but I warn you, Mycroft won't give in without a fight.'

'What did he say to you in the car?'

'Very little, it was more of an interrogation really. He wanted to know everything that I knew about you - when I'd met you, what I thought of you professionally, what I knew about your past relationships, how you'd met Sherlock, what I thought of your relationship, why I thought that you were with him - everything.'

Kate groaned and buried her head in her hands for a minute. 'What did you say?' she asked, without looking up.

'I gave him my honest opinion, there seemed no reason not to. Do you mind?'

'Not if it was good, no.' She said, looking up at him with a grin.

'Of course it was good. I told him that I thought that you were a fantastic doctor, caring, compassionate, but with enough bite to stand up to the punters when you had to. I told him that I'd never seen Sherlock happier or more stable.'

'Did he believe you?'

'Hard to tell with Mycroft, but he'll still want to talk to you. In fact he asked me to try to persuade you to contact him.'

'And is that why you tried to do just that?' Kate was aware that she sounded suspicious, despite her best intentions.

'No, of course not!' John said, exasperated. 'I'm giving you my honest opinion, as a friend. The best thing, for you and for Sherlock would be for you to talk to Mycroft before he comes to you. But I get it, Kate, I completely get why you won't do that without discussing it with Sherlock.'

Kate shook her head, 'What a mess,' she said.

'So tell me about the case,' John said finally after they had sat in silence for several minutes.

'Interesting one really. GCHQ analyst, disappeared ten days ago. One day he was at work as normal, the next morning he just never turned up, and he hasn't been seen since. CCTV cameras captured him walking into the tube at Pimlico, then after that - nothing. He just disappeared.'

'No signs that he could have been abducted ?'

'No, nothing. They've checked all of the tube footage for every station in London, nothing.'

'So he left the tube by another way - old fire tunnels, or service tunnels may be?'

'Must have done, but the question is why. There was no history of him acting oddly, nothing seems to have gone from his flat, passport is still there, everything. He literally walked out of his life in just the clothes that he was wearing.'

'So what have you got so far?'

'Come back into the lab with me and I'll show you.' Kate said, relieved to have diverted the topic of conversation away from Mycroft Holmes at last.